期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2015
卷号：112
期号：12
页码：3606-3611
DOI：10.1073/pnas.1424962112
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceUndulating swimmers, such as worms, are ubiquitous and play important roles in the ecosystem; agriculture; human, animal, and plant health; and medical research. The ability of undulatory swimmers to align against the flow (rheotax) is important in the animals' life cycles, enabling them to navigate their environment and to maintain their positions in the presence of adverse flows such as in the hosts' guts and blood vessels. We elucidate, for the first time to our knowledge, the mechanism responsible for rheotaxis in low-Reynolds-number, undulatory swimmers. This knowledge will provide a better understanding of the animals' life cycles, will enable the development of strategies to disturb their life cycles, and will improve the design of microfluidic devices for biological research. The ability to orient oneself in response to environmental cues is crucial to the survival and function of diverse organisms. One such orientation behavior is the alignment of aquatic organisms with (negative rheotaxis) or against (positive rheotaxis) fluid current. The questions of whether low-Reynolds-number, undulatory swimmers, such as worms, rheotax and whether rheotaxis is a deliberate or an involuntary response to mechanical forces have been the subject of conflicting reports. To address these questions, we use Caenorhabditis elegans as a model undulatory swimmer and examine, in experiment and theory, the orientation of C. elegans in the presence of flow. We find that when close to a stationary surface the animal aligns itself against the direction of the flow. We elucidate for the first time to our knowledge the mechanisms of rheotaxis in worms and show that rheotaxis can be explained solely by mechanical forces and does not require sensory input or deliberate action. The interaction between the flow field induced by the swimmer and a nearby surface causes the swimmer to tilt toward the surface and the velocity gradient associated with the flow rotates the animal to face upstream. Fluid mechanical computer simulations faithfully mimic the behavior observed in experiments, supporting the notion that rheotaxis behavior can be fully explained by hydrodynamics. Our study highlights the important role of hydrodynamics in the behavior of small undulating swimmers and may assist in developing control strategies to affect the animals' life cycles.
关键词：rheotaxis ; hydrodynamics ; C. elegans ; nematode ; microfluidics
